An electron beam apparatus such as a scanning electron microscope obtaining a scanning image of a sample by scanning a primary electron beam on the sample is used for a purpose of pattern evaluation such as inspection or measurement of a micropattern in a semiconductor device. The apparatus of such a kind comprises an image shift function for electrically shifting an electron beam irradiation area (a field of observation view) within a range of several μm to 10 μm by electrically deflecting the primary electron beam in order to shift the field of observation view to an evaluation point with high accuracy.
On the other hand, in a scanning electron microscope used for a general-purpose observation of a general sample, a field of observation view is mainly shifted by mechanically shifting a sample stage. However, because the mechanical shifting of the stage becomes difficult when the magnification of observation is high, image shift is used in order to shift a field of observation view to the observation center. In this case, since the field of observation view can be more speedily shifted in a wide range, as the shifting amount of the field of observation view by the image shift is larger, operability of the apparatus can be improved.
Further, in the measurement of semiconductors or high-technology materials, a low acceleration voltage lower than several kV is generally used in order to prevent samples from being charged, and necessity of performing nanometer order observation is increasing. Therefore, in order to improve the resolution under the low acceleration voltage by reducing the aberration of the objective lens, the scanning electron microscope for this purpose is used by shortening the focal distance of the objective lens, or by applying a negative voltage to the sample (retarding method).
In the retarding method of applying a negative voltage to the sample, secondary electrons generated from the sample are accelerated by the voltage applied to the sample to travel to the upper portion of the objective lens. Therefore, as described in the specification of U.S. Pat. No. 2,821,153, by producing an electric field and a magnetic field intersecting each other at right angle (an E×B field) in the upper portion of the objective lens, the path of the secondary electrons generated from the sample is deflected to be separated from the path of the primary electrons traveling from an electron source, and thus the secondary electrons are detected by a secondary electron detector in high efficiency. Further, The specification of U.S. Pat. No. 2,821,153 discloses a method in which in order to eliminate the chromatic aberration produced by the E×B field, another E×B field is provided in the side of the electron source at a position closer to the electron source than the E×B field for deflecting the secondary electron, and the chromatic aberration of the E×B (E-cross-B) field for deflecting the secondary electron is canceled by the chromatic aberration produced by the E×B field provided in the side of the electron source. However, in the technology described in the specification if U.S. Pat. No. 2,821,153, the energy dispersion to be corrected is only the energy dispersion produced in the deflection direction (only a single direction) of the secondary electrons.
The image shift function for shifting the field of observation view in an arbitrary direction by an arbitrary amount by electrically deflecting the primary electron beam is a function indispensable to the electron beam apparatus for obtaining a scanning image with high resolution and in high magnification, as described above. However, when image shift is performed, the primary electron beam is energy-dispersed corresponding to the amount of image shift in the shift direction to cause degradation in the resolution. The degradation in the resolution becomes an un-negligible problem as the resolution of the apparatus is increased.